1. Field of the Invention (Technical Field)
This invention pertains to the field of microwave or radio frequency technology. More particularly, the invention pertains to a unique antenna called the split waveguide antenna that permits the radiation of high peak power electromagnetic fields at radio frequencies.
2. Background Art
Antennas are transducers that convert guided electromagnetic energy to radiated energy; they send out electromagnetic energy such that it is transmitted and spreads into a surrounding medium such as the atmosphere. Antennas were first intentionally employed by Heinrich Hertz in 1885 to demonstrate the transmission and radiation of electromagnetic energy across large distances. Since that time antennas have been designed for many specialized purposes, including communications, RADAR, directed energy (for military and medical purposes), and others too numerous to list or enumerate. For applications that involve low radiated RF power levels electrically small (in terms of the wavelength of the operating frequency) antennas can be used. However, it is difficult to radiate high powers (where electrical breakdown phenomena are observed) from electrically small antennas. This is because the energy density becomes large enough to cause either field emission from surfaces within the confines of or on the antenna, or breakdown in the medium surrounding the antenna, or both phenomena. Disclosed is a unique way to radiate high power electromagnetic fields from a compact and conformal antenna. By compact and conformal, it is meant, an antenna that can be deployed on or aboard weight and/or volume sensitive platforms, such as on or aboard the external stores of manned fighter aircraft such as an F-16 or F-15, or aboard an unmanned aerial vehicle such as the X-45.
There are several prior art devices that attempt to solve the problem of radiating high power from electrically small antennas. However, the shortcomings of each of the attempted solutions, is evident. U.S. Pat. No. 6,559,807 to Koslover describes a technique for realizing a high-power microwave device that includes an antenna. The antenna consists of a feed horn and two reflecting surfaces. The excitation of the radiating antenna is made through a single feed horn, and thus its power rating or capability is limited by the power capacity of the feed horn. Furthermore, the invention describes the use of multiple reflecting surfaces that are each many wavelengths in cross section. They claim that this high-power microwave device and antenna are suitable for fixed winged aircraft such as the Boeing 747 and DC-10. It is clearly not suitable for small air platforms.
U.S. Pat. No. 6,211,837 to Crouch, et al., discloses an antenna system and technique for radiating intense electromagnetic fields at L-band frequencies. The geometry of the system comprises a circular waveguide transmission line feed, conical horn transition section, and circular radiating aperture with inner and outer windows. The circular waveguide transmission line supplies and propagates the electromagnetic energy in the TM01 mode. The electromagnetic field is subsequently transported to the radiating aperture of the antenna by the conical horn section and has a TM01-like field distribution. It is well known that an antenna aperture with the TM01-like field distribution will result in a low gain radiation pattern. An actual antenna, based on the concepts described in this patent, was built to operate at L-band to radiate RF field with peak power levels of approximately 1 GW (RMS). It is known that the resulting antenna failed to radiate this level of RF power without breakdown.
Recently, Koslover, U.S. Pat. No. 5,323,169, and Baum, C. E. Baum, “Some Features of Waveguide/Horn Design,” Sensor and Simulation Note 314, 22 Mar. 1989, have described methods to partition parallel plate and rectangular waveguide transmission lines carrying intense electromagnetic fields in a manner that preserves the propagating mode, minimizes or eliminates reflections and does not result in electrical breakdown.
Recently, Baum, C. E. Baum, “High-Power Scanning Waveguide Array,” Sensor and Simulation Note 459, 18 Dec. 2001, described the partition of a rectangular aperture into sub-apertures for purposes of increasing the power capacity and mechanical strength of an aperture.
None of these devices; however, disclose or teach the use of an antenna that is concurrently high-power capable, compact and conformal, scalable to arbitrary power levels, and produces a high gain radiated pattern with high aperture efficiency.